Joint for coaxial electrical cables



Oct. 27, 1953 R. c. MILDNER ET AL 2, 7,

JOINT FOR COAXIAL ELECTRICAL CABLES Filed Feb. 27. 1950 '9 a 3 Q 2 0 a Oa w I &7 'H' w w 5! N a A N W =& w I

Patented Oct. 27, 1953 UNITED QFEICE JOINT For COAXIAL trcre cet CABLES.

Application February 27, 1950, Serial No. 146,568 In Great BritainFebruary 28, 1949 i c ams men of cable together is two-fold. Aluminiumis 3 coming more into use in place of lead for the sheathing of cableswith solid dielectric, and the temperature required for making a weldedaluminium joint is usually too high for the insulation protected by thesheath. Moreover, the conductors inside the sheath must of necessity beexposed for the purpose of jointing, and then a gap is left in thesheath, over which a piece of protective material must be provided tocover the joint and to form the metallic 'bond between the sheaths ofthe two ends of cable.

In the case of co-axial cable the central cone ductor has to be jointed,for which purpose a space must also be left between the ends of the twoouter conductors to provide access. then required to bridge the gapbetween the ends of the outer conductors in such a manner as toconstitute the equivalent of a straight throughconductor. Now, with thehigh frequencies transmitted along co-axial cables it is important thatthe characteristic impedance should remain uniform along the cable andthrough the joint. If there is any change in the bore of the outerconductor or any lack of electrical continuity, there is an abruptchange of characteristic ime pedance, which would cause disturbingreflections of the current being transmitted.

It is known that two pipes may be coupled to-. gether by a main couplingelement having both ends tapered internally and a shoulder at each endagainst which the respective pipes can butt. A flanged nut screwed oneach end of the coupling element drives a metallic packing ring intoengagement with the outer surface of the pipe by pressing it into theflared end of the coupling element. Where the pipe has nothing in-: sideit and is destined to carry a liquid or gas, no difiiculty arises inassembling the joint. Where, however, there is something inside the pipeor tubular member such as another conduc: tor, the inner conductors mustbe jointed, and it is not possible for performing this operation tothread the coupling member on to the pipe or tubular member to bejointed, because its bore is made equal to the bore of the pipe.

It is cc rdin t t in ent on a o nt b tw tw en hs. o tub la c nduct r shrq ndin one or more ther c d hr cm is a ccupling element having aninternal bore of a diameter to pa s o er th tu ar c nducto nd havi bothends. f ar d interna ly. a ve split axially to fit inside t ma c up ngel men over the joint of the inner conductor or conductors and t0. "bu ta ainst the r spect e en s of the tubular cond c or, a meta lic pack grin at each end adapted to b f rc d in en a ement with the outer surfaceof the tubular conductor when driven into the flared. end of the maincousling lement, and a flange nut s rewed on e ch end of the maincouplin element t force t e respective packing rin 1111 0 th Sai flarednd- The invention is illustrated by the accompanyins draw n which sh wsa lon itudi al Se t thro h a ic nt b tw en We e th of coaxia cable inaccordance with the invention.

Referrin to the draw ng. th c -axia ables. to h Jo n ed a h cqmpr se ani n r o r od ccniiu cr i. out r a umi ium heath 3 can.- entrie with theconductor wh ch n it te the cute cn uct d l t eh p er 9 th mh es t9 ma nn th conduc s? I rul centra w th the sh a h 2 hr ue'hcu th l n h if thecab en i su atin himb str tur i shown at 3 and ha it class sh e t a toresnon ine adjacen thimhles 5a and 3b f which parts y a e .shcw h i ercc duc s l a d ille and t d a ia a h i end .0118 w th le t-han ed th ad.t o h w h r thande A. ferrul 4 h s a head of h ame diameter as theconductor 5 and projecting thereom in opp site di inns s e threads at0p: pos an to en r th ta p d ho es in th two conductors I. 2

T ake the J nt in h nn r co d tor the tw -cndu qr ends a e, bro h int cn a t wi h the ends of he s r wed por ions of the 61? rule 5. The headof the ferrule is then turned until both conductor ends are against theshoul-v ders of the ferrule adjacent to the screw threaded portions. Injointing the inner conductor in this manner a gap has of necessity beenleft be-v tween the ends of the outer conductor, which must be filled upwhen jointing the two ends to: ecth r.

The joint for the outer conductor comprises a ma n cq pl ns e ment 5 ofsuf iciently large bore to slip over the sheath 2, together with two nur en was 6 s r wed on to the ends of the elemen 5 and also of a bore tofit over the sheath 2- To 1111 up the gap between the adjacent sheathends and to provide a bore equal to that of the sheath, a sleeve '1 ismade in two halves by a longitudinal slit along a diametral plane. Thesleeve 7 has bore and outside diameter respectively equal to those ofthe sheath 2. For securing the joint firmly there is at each end ametallic ring 8 of a somewhat flexible metal rather harder than thesheath 2. Each ring 8 comprises a curved body portion 8a and enlargedfoot 81) 1 having a conical face 80 for engagement with the interiorshoulder of the flanged nut 6. At its other end the body portion 8atapers off to a knife edge 86 so that when the nut 6 is screwed home, ashereinafter explained, the curved outer face of the body portion 8a willbe driven against a tapered seating 5a on the main coupling element 5whereby the knife edge 8e will be caused to bite into the surface of theouter conductor.

To make a joint between two lengths of coaxial cable, the nut or end cap6 and ring 8 are threaded in that order on to one cable end, while theother end cap 6, packing ring 8 and the coupling element 5 are threadedon to the other cable end. The inner conductors I after having beenprepared are joined by means of the ferrule 4 to constitute a singleconductor of uniform outside diameter. Thereupon the two halves of thesleeve 1 are put into place, the cable ends having been cut in such amanner that the sleeve will just fit between the two opposed ends of thesheath 2. An extra polythene thiinble 3 in addition to those in thecable will have been placed in the cable before jointing the inner pconductor l and will form a support for the half sleeves I.

The parts threaded on to the outer conductor are then brought togetherinto their right position on the cable, and the two end caps are screwedup tight on to the main coupling element 5. The inner ends of the rings3 are pressed inwards by this action and embed themselves in therespective portions of the outer conductor or sheath 2. At the same timethe screwing up of the end caps 6 tends to draw the ends of the sheath 2towards each other, whereby the sleeve is tightly gripped at the endsand there is produced in effect a continuous outer conductor at thejoint of the same bore as the outer conductor of the two cables.

The sleeve "2' if split into two parts should be split accurately on thediameter. Alternatively, it may be split into more than two parts. Allthe parts can then be located by the polythene thimble Again it could besplit at one position only, being sprung into position after the innerjoint is completed.

Where a joint of the kind described is used for a cable with solidinsulation, whether for an active outer conductor or a protectivesheath, the procedure is somewhat similar. The parts as described arethreaded on to the respective cable ends. The internal conductors arejointed and then the split sleeve is put into position and the jointtightened up by means of the nuts 6.

It is usually advantageous to make the inner ends of the rings 8serrated in order to assist them in biting into the sheath 2. Electricalcontinuity is thereby more certainly ensured.

Holes are provided in the thimble structure 3 and in the thimbles 3a and3b to permit the passage of air or gas through the cable. The thirnble3b is shown as being provided with such holes, designated H. Holes inthe thimble structure 4 3 and the thimble 3a are not shown because ofthe positions of these parts relative to the plane of the section shownin the drawing.

What we claim is:

1. In a concentric conductor transmission line having adjacent lengthsof tubular outer conductors having opposed ends, joined lengths of innerconductors therein, nuts surrounding opposed ends of said outerconductors and having internal chamfered faces, a coupling elementbetween. said opposed ends and being screwthreaded to said nuts andprovided internally at each of its ends with a chamfered jointingsurface, a split conductor sleeve shorter than and located within saidcoupling element and whose internal and external diameters are of thesame dimension as those of the outer conductors, the opposite ends ofsaid split sleeve being in abutting engagement with the adjacent ends ofsaid outer conductors, said split sleeve enclosing the joint of theinner conductors, and packing rings each having an end engaged with thechamfered faces of the nuts for axial movement of the rings toward eachother by the nuts, and each ring having the other end of knife-likeshape so that on said axial movement through tightening the nuts, thepacking rings will be deflected inwards by said chamfered jointingsurfaces into biting engagement with the adjacent tubular outerconductor to force the same into abutting engagement with said sleeve.

2. A structure as defined in claim 1 in which the coupling element hasinteriorly tapered ends and in which the knife-like edges of the packingrings are serrated.

3. A structure as defined in claim 1 in which the sleeve has the samebore as each tubular conductor.

l. A structure as defined in claim 1 in which the sleeve has the samebore as each tubular conductor, and in which the inner conductor isjointed by means of a ferrule having right and left-handed threads toengage the conductor links and a head of the same external diameter asthe inner conductor.

5. A joint as defined in claim 1 in which the sleeve is split on adiametral plane into two parts.

6. In a concentric conductor transmission line having tubular outerconductors having opposed ends and a gap therebetween, inner conductorswithin the outer conductors joined at the gap, nuts surrounding opposedends of said outer conductors and having internal chamfered faces, acoupling element between said opposed ends and being screw-threaded tosaid nuts and provided internally at each of its ends with a charm--fered jointing surface, a split conductor sleeve shorter than andlocated within said coupling element and Whose internal and externaldiameters are of the same dimension as those of the outer conductors,the opposite ends of said split sleeve being in abutting engagement withthe adjacent ends of said outer conductors, insulation within the splitconductor sleeve centering the inner conductors and alining said splitconductor sleeve with said outer conductors, and packing rings eachhaving an end engaged with the chamfered races of the nuts for axialmovement of the rings toward each other by the nuts, and each ringhaving the other end of knife-like shape so that on said axial movementthrough tightening the nuts, the packing rings will be deflected inwardsby said charnfered jointing surfaces into biting engagement with theadjacent tubular outer conductor to force the same into abuttingengagement with said sleeve.

7. In a concentric conductor transmission line having tubular outerconductors having opposed ends and a gap therebetween, inner conductorsWithin the outer conductors joined at the gap, nuts surrounding opposedends of said outer conductors and having internal chamfered faces, acoupling element between said opposed ends and being screw-threaded tosaid nuts and provided internally at each of its ends with a chamferedjointing surface, a split conductor sleeve shorter than and locatedwithin said coupling element and internal and external diameters are ofthe same dimension as those of the outer conductors, the opposite endsof said split sleeve being in abutting engagement with the adjacent endsof said outer conductors, an insulating thimble structure within thesplit conductor sleeve centering the inner conductors and alining saidsplit conductor sleeve with said outer conductors, insulation thimblesrespectively within said opposed ends of said outer conductors, saidinsulating thimble structure at its ends being in intertting engagementwith said insulation thimbles RAYMOND CHARLES MILDNER. CLIVE EDWARDCHRISTOPHER LOVELACE.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,110,421 Moody Mar. 8, 1938 2,156,772 Seeley May 2, 19392,207,522 Smith et a1. July 9, 1940 2,209,152 Daniels July 23, 19402,497,706 Wetherill Feb. 14, 1950 2,530,153 Davey et a1 Nov. 14, 1950

